Startup culture ‘assembly line’ product development IMO.

The indie hacker approach to this is constantly develop, deploy and monitor. If the feature is used, improve it. If the feature is unsuccessfully used, improve it. If the feature isn't used, kill it. This is heavily data-driven and requires intuition for users' desires (what they want, how they want it) and your product. The latter takes years to learn.

Indie hacker? Isn’t that just the approach of a good development team, solo or multi-person, in general?

When working for companies the development process is longer and requires input from multiple stakeholders outside of the development team, e.g. product manager, project manager, copy writes. There is a substantial analysis before starting the development. As an independent hacker (indie hacker) you don't have those resources but instead increased agility and speed.